Subjects

Paired associative stimulation (PAS) combining repeated pairing of electrical stimulation of a peripheral nerve with transcranial magnetic stimulation (TMS) over the primary motor cortex (M1) can induce neuroplastic adaptations in the human brain and enhance motor learning in neurologically-intact individuals. However, the extent to which PAS is an effective technique for inducing associative plasticity and improving motor function in individuals post-stroke is unclear. Objective: The objective of this pilot study was to investigate the effects of a single session of PAS to modulate corticomotor excitability and motor skill performance in individuals post-stroke. Methods: Seven individuals with chronic stroke completed two separate visits separated by at least one week. We assessed general corticomotor excitability, intracortical network activity and behavioral outcomes prior to and at three time points following PAS and compared these outcomes to those following a sham PAS condition (PAS SHAM). Results: Following PAS, we found increased general corticomotor excitability but no significant difference in behavioral measures between PAS conditions. There was a relationship between PAS-induced corticomotor excitability increase and enhanced motor skill performance across post-PAS testing time points. Conclusion: These results provide preliminary evidence for the potential of PAS to increase corticomotor excitability that could favorably impact motor skill performance in chronic individuals post-stroke and are an important first step for future studies investigating the clinical application and behavioral relevance of PAS interventions in post stroke patient populations.

Subjects

Peripheral nerve injuries are common, and functional recovery is very poor. Beyond surgical repair of the nerve, there are currently no treatment options for these patients. In experimental models of nerve injury, interventions (such as exercise and electrical stimulation) that increase neuronal activity of the injured neurons effectively enhance axon regeneration. Here, we utilized optogenetics to determine whether increased activity alone is sufficient to promote motor axon regeneration. In thy-1-ChR2/YFP transgenic mice in which a subset of motoneurons express the light-sensitive cation channel, channelrhodopsin (ChR2), we activated axons in the sciatic nerve using blue light immediately prior to transection and surgical repair of the sciatic nerve. At four weeks post-injury, direct muscle EMG responses evoked with both optical and electrical stimuli as well as the ratio of these optical/electrical evoked EMG responses were significantly greater in mice that received optical treatment. Thus, significantly more ChR2+ axons successfully re-innervated the gastrocnemius muscle in mice that received optical treatment. Sections of the gastrocnemius muscles were reacted with antibodies to Synaptic Vesicle Protein 2 (SV2) to quantify the number of re-occupied motor endplates. The number of SV2+ endplates was greater in mice that received optical treatment. The number of retrogradely-labeled motoneurons following intramuscular injection of cholera toxin subunit B (conjugated to Alexa Fluor 555) was greater in mice that received optical treatment. Thus, the acute (1 hour), one-time optical treatment resulted in robust, long-lasting effects compared to untreated animals as well as untreated axons (ChR2-). We conclude that neuronal activation is sufficient to promote motor axon regeneration, and this regenerative effect is specific to the activated neurons.

Subjects

Objective: To examine the association between long-term metformin therapy and serum vitamin B12 monitoring. Design: Retrospective cohort study. Setting: A single Veterans Affairs Medical Center (VAMC), 2002–2012. Participants: Veterans 50 years or older with either type 2 diabetes and long-term metformin therapy (n = 3,687) or without diabetes and no prescription for metformin (n = 13,258). Measurements: We determined diabetes status from outpatient visits, and defined long-term metformin therapy as a prescription ≥500 mg/d for at least six consecutive months. We estimated the proportion of participants who received a serum B12 test and used multivariable logistic regression, stratified by age, to evaluate the association between metformin use and serum B12 testing. Results: Only 37% of older adults with diabetes receiving metformin were tested for vitamin B12 status after long-term metformin prescription. The mean B12 concentration was significantly lower in the metformin-exposed group (439.2 pg/dL) compared to those without diabetes (522.4 pg/dL) (P =.0015). About 7% of persons with diabetes receiving metformin were vitamin B12 deficient ( < 170 pg/dL) compared to 3% of persons without diabetes or metformin use (P =.0001). Depending on their age, metformin users were two to three times more likely not to receive vitamin B12 testing compared to those without metformin exposure, after adjusting for sex, race and ethnicity, body mass index, and number of years treated at the VAMC. Conclusion: Long-term metformin therapy is significantly associated with lower serum vitamin B12 concentration, yet those at risk are often not monitored for B12 deficiency. Because metformin is first line therapy for type 2 diabetes, clinical decision support should be considered to promote serum B12 monitoring among long-term metformin users for timely identification of the potential need for B12 replacement.

Subjects

Axonal degeneration is a common pathologic feature in peripheral neuropathy, neurodegenerative disease, and normal aging. Oxidative stress may be an important mechanism of axonal degeneration, but is underrepresented among current experimental models. To test the effects of loss of the antioxidant enzyme Cu,Zn-superoxide dismutase (SOD1) on axon survival, we cultured dorsal root ganglion (DRG) neurons from SOD1 knockout mice. Beginning as early as 48-72 h, we observed striking degeneration of Sod1-/- axons that was prevented by introduction of human SOD1 and was attenuated by antioxidant treatment. To test susceptibility to increased superoxide production, we exposed wild-type DRGs to the redox-cycling herbicides paraquat and diquat (DQ). Dose-dependent axon degeneration was observed, and toxicity of DQ was exacerbated by SOD1 deficiency. MTT staining suggested that DRG axons are more susceptible to injury than their parent cell bodies in both paradigms. Taken together, these data demonstrate susceptibility of DRG axons to oxidative stress-mediated injury due to loss of SOD1 or excess superoxide production. These in vitro models provide a novel means of investigating oxidative stress-mediated injury to axons, to improve our understanding of axonal redox control and dysfunction in peripheral neuropathy.

Subjects

After peripheral nerve injury, neurotrophins play a key role in the regeneration of damaged axons that can be augmented by exercise, although the distinct roles played by neurons and Schwann cells are unclear. In this study, we evaluated the requirement for the neurotrophin, brain-derived neurotrophic factor (BDNF), in neurons and Schwann cells for the regeneration of peripheral axons after injury. Common fibular or tibial nerves in thy-1-YFP-H mice were cut bilaterally and repaired using a graft of the same nerve from transgenic mice lacking BDNF in Schwann cells (BDNF-/-) or wild-type mice (WT). Two weeks postrepair, axonal regeneration into BDNF-/-grafts was markedly less thanWTgrafts, emphasizing the importance of Schwann cell BDNF. Nerve regeneration was enhanced by treadmill training posttransection, regardless of the BDNF content of the nerve graft. We further tested the hypothesis that traininginduced increases in BDNF in neurons allow regenerating axons to overcome a lack of BDNF expression in cells in the pathway through which they regenerate. Nerves in mice lacking BDNF in YFP+neurons (SLICK) were cut and repaired with BDNF-/-and WT nerves. SLICK axons lacking BDNF did not regenerate into grafts lacking Schwann cell BDNF. Treadmill training could not rescue the regeneration into BDNF-/-grafts if the neurons also lacked BDNF. Both Schwann cell- and neuron-derived BDNF are thus important for axon regeneration in cut peripheral nerves.

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Seeding nerve guidance conduits with Schwann cells can improve the outcome of peripheral nerve injury repair. Bone marrow stem cells (BMSCs) represent a good choice of cell source as they can differentiate into Schwann cells under appropriate conditions. In this work, we systematically investigated the differentiation of BMSCs into Schwann cells on scaffolds comprising electrospun fibers. We changed the alignment, diameter, and surface properties of the fibers to optimize the differentiation efficiency. The uniaxial alignment of fibers not only promoted the differentiation of BMSCs into Schwann cells but also dictated the morphology and alignment of the derived cells. Coating the surface of aligned fibers with laminin further enhanced the differentiation and thus increased the secretion of neurotrophins. When co-cultured with PC12 cells or chick dorsal root ganglion, the as-derived Schwann cells were able to promote the outgrowth of neurites from cell bodies and direct their extension along the fibers, demonstrating the positive impacts of both the neurotrophic effect and the morphological contact guidance. This work offers a promising strategy for integrating fiber guidance with stem cell therapy to augment peripheral nerve injury repair.

Subjects

Among responders to microbial invasion, neutrophils represent one of the earliest and perhaps most important factors that contribute to initial host defense. Effective neutrophil immunity requires their rapid mobilization to the site of infection, which requires efficient extravasation, activation, chemotaxis, phagocytosis, and eventual killing of potential microbial pathogens. Following pathogen elimination, neutrophils must be eliminated to prevent additional host injury and subsequent exacerbation of the inflammatory response. Galectins, expressed in nearly every tissue and regulated by unique sensitivity to oxidative and proteolytic inactivation, appear to influence nearly every aspect of neutrophil function. In this review, we will examine the impact of galectins on neutrophils, with a particular focus on the unique biochemical traits that allow galectin family members to spatially and temporally regulate neutrophil function.

Article

Injuries to the peripheral nervous system are major sources of disability and often result in painful neuropathies or the impairment of muscle movement and/or normal sensations. For gaps smaller than 10 mm in rodents, nearly normal functional recovery can be achieved; for longer gaps, however, there are challenges that have remained insurmountable. The current clinical gold standard used to bridge long, nonhealing nerve gaps, the autologous nerve graft (autograft), has several drawbacks. Despite best efforts, engineering an alternative "nerve bridge" for peripheral nerve repair remains elusive; hence, there is a compelling need to design new approaches that match or exceed the performance of autografts across critically sized nerve gaps. Here an immunomodulatory approach to stimulating nerve repair in a nerve-guidance scaffold was used to explore the regenerative effect of reparative monocyte recruitment. Early modulation of the immune environment at the injury site via fractalkine delivery resulted in a dramatic increase in regeneration as evident from histological and electrophysiological analyses. This study suggests that biasing the infiltrating inflammatory/immune cellular milieu after injury toward a proregenerative population creates a permissive environment for repair. This approach is a shift from the current modes of clinical and laboratory methods for nerve repair, which potentially opens an alternative paradigm to stimulate endogenous peripheral nerve repair.